Antiperspirant compositions are widely employed throughout many parts of the world in order to control localised perspiration and thereby avoid wet patches which many societies consider to be unsightly, for example in axillary regions (the underarm) and less commonly to feet or other occluded body regions. Such compositions usually employ an astringent metal salt, such as most often an aluminium or aluminium/zirconium salt. Such salts are not only capable of blocking pores to inhibit and reduce sweating, but are also microbicidal and a significant fraction of the salts commonly remain on the skin surface between pores. By controlling perspiration with such salts, the user advantageously can simultaneously reduce or eliminate malodour generated locally. Accordingly, if insufficient antiperspirant active is present to enable the composition to function as an effective antiperspirant, the active normally provides deodorancy benefits.
Antiperspirant compositions containing effective concentrations of such astringent salts have been made or proposed in a range of different forms, for topical application, applied via non-contact applicators including liquid pump or squeeze sprays and aerosols, or via contact applicators including roll-ons for liquids, dispensers where a cream or gel is extruded through a narrow slit or aperture and sticks in which a solid is advanced though a wide aperture, often by an elevator coupled to a mechanism for advancing the elevator. A significant proportion of such compositions additionally comprise a carrier liquid for the antiperspirant active material. The liquid can be water-immiscible, in which case the antiperspirant can be present in particulate form suspended within the water-immiscible liquid. If desired, the carrier liquid can also be e thickened or solidified to form either a cream or a firm solid. Anhydrous creams are sometimes called soft solids, because unlike firm solids, they can be extruded under low force through narrow slits or apertures. In one class of products, of particular relevance to the present invention, the carrier fluid is structured or gelled to create a solid, which is commonly produced in the form of a stick, the stick usually, but not always, being housed within a dispensing container.
One aspect of consumer products to which consumers pay especial attention is the appearance of the product after application and likewise its sensory attributes. In addition, attention is often paid to the product before application. Many conventional antiperspirant products in stick or soft solid form that are distributed in the market place are opaque, white in appearance in the applicator pack and some of these are also white when applied onto the skin. Over the last 10 to 15 years, antiperspirant composition manufacturers have sought to offer alternative formulations, or at least publish such formulations in patent or other literature, which address one or other of the problems associated with avoiding white products, be they in the pack or after application onto the skin.
The principle has been disclosed by Vu et al in U.S. Pat. No. 5,384,117 of refractive index matching a suspended particulate antiperspirant active salt with a carrier liquid within about 0.02 units so as to achieve a relative turbidity of less than 800 FTU. In order to thicken or solidify the carrier liquid, he suggested employing a polymer as structurant (gellant) and employed in worked examples a polyethylene-vinyl acetate copolymer together with an aluminium chlorohydrate antiperspirant active. This structurant had a refractive index which was quite close to that of the other constituents. The choice of antiperspirant active exemplified, aluminium chlorohydrate, has a comparatively low refractive index, so that Vu did not provide suitable guidance as to how to achieve suitable clarity for compositions across his entire range and particularly for compositions containing an active with a higher refractive index, such an aluminium-zirconium actives. By comparison with Vu, it is desirable to employ alternative structurants that do not need to-be refractive index matched with the carrier liquid and suspended solid. If the polyethylene-vinyl acetate copolymer were used to solidify a composition employing a liquid carrier having a high refractive index that is suitable for aluminium zirconium actives, he would not achieve a translucent product, because there would be too great a disparity in refractive indexes of the carrier liquid and the structurant. Vu et al does not contemplate any problems arising from choice of a class of gellant that he does not mention or the effect of particle size distribution of the suspended particulate material and accordingly does not contemplate or even foreshadow the present invention.
Unilever has previously disclosed in WO 03/059308 that even if there is refractive index matching of the antiperspirant active particles and the gelled carrier liquid in which they are suspended, there can still be no guarantee of translucency. WO 03/059308 discloses that the particle size distribution of a suspended antiperspirant active can affect the clarity of a formulation in which it is suspended, the formulation advantageously comprising a carrier liquid of which at least 50% by weight comprises a non-volatile silicone oil and alkyl-aryl ester oil and which is solidified with a non-polymeric fibre-forming structurant. The text discloses that it is beneficial to select an antiperspirant solid of which less than 50% by weight of the particles have a diameter of up to 10 μm.
Further investigations into anhydrous antiperspirant sticks that compositions containing antiperspirant with a high proportion of comparatively large particles can suffer from other problems, including in particular segregation when a highly desirable class of gellants is employed.
One class of non-polymeric structurants which it is advantageous to employ to produce anhydrous antiperspirant sticks and particular anhydrous translucent sticks comprises fibre-forming amide gellants, but such gellants tend to have a high dissolution temperature in hydrophobic liquids that are employed in anhydrous antiperspirant formulations, and in particular in silicone oils and aryl-containing ester oils, the types of oils that enable a high refractive index carrier liquid to achieve translucency across a wide range of antiperspirant actives.
In the manufacture of anhydrous antiperspirant sticks a mixture of the gellant and the carrier liquid is fluidised by heating the mixture until the gellant melts/dissolves, the particulate antiperspirant active is mixed in, commonly after gellant dissolution, and the fluid mixture is thereafter filled into a mould or more usually directly into a dispensing container in which it cools to below its solidification temperature. The fluid mixture formulation is conventionally rendered homogenous in its processing vat or in distribution pipework by being mixed or otherwise subjected to shearing render, but once in the container the composition becomes quiescent because it is no longer practical to shear or mix the formulations. The instant inventors have found that the solidification temperature of anhydrous formulations gelled by fibre-forming amide gellants is sensitive to shearing, there being a significant drop in the solidification temperature from when compositions are being sheared to the same composition under quiescent conditions. Accordingly, since the temperature of the composition in the processing vat must be maintained above the shearing solidification temperature to avoid premature solidification, a larger temperature drop occurs in the container after filling to reach the quiescent solidification temperature. Comparatively large particles have a greater tendency to settle in quiescent liquid media than do smaller sized particles, so that a consequence of employing the larger sized antiperspirant particles (desirable to enhance translucency) with the combination of chosen carrier liquid and gellant is that there is a significant risk of segregation before the formulation solidifies or the viscosity of the suspending carrier fluid has increased to such an extent that particle settling is slowed sufficiently to prevent undue settling.
The employment of N-acyl aminoacid amide gellants to solidify oil compositions has been disclosed previously in U.S. Pat. No. 3,969,087 and specifically antiperspirant compositions in US 2002/0159961, US 2004/0229984, WO 2004/098552 and WO 2004/098553. Antiperspirant compositions in which an oil phase is solidified with selected dipeptide gellants are described in WO 03/059306 and WO 03/059307. Antiperspirant compositions in which an oil phase is solidified with selected bis amido gellants and particularly gellant derive from 1,2 or 1,3 bis amidocyclohexane are described in U.S. Pat. No. 6,410,003. Formulations in which amide derivatives of di and tribasic carboxylic acids gel an oil phase are described in U.S. Pat. No. 5,840,288 and U.S. Pat. No. 6,190,673B1. None of these specifications contemplate particle segregation when employing comparatively large antiperspirant particles, nor any means to ameliorate or overcome segregation.
Accordingly, it is an object of the present invention to identify means to ameliorate or overcome settling of a particulate antiperspirant in a carrier liquid comprising a silicone and/or aryl-containing ester oil that is gelled with a fibre-forming amide gellant.